Mental Effort

of the semantic features of the stimulus, a binary decision, and response selection. Name-Match RT is significantly longer than Physical-Match RT. Significant differences have also been found between subjects of high and low verbal ability, and RT in a modified version of the Posner paradigm has been found to significantly correlate (negatively) with intelligence. Inspection Time. Although research on inspection time (IT) has been traced to James McKeen Cattell in the 1880s, contemporary interest in IT stems from the work of Vickers, Nettelbeck and their colleagues (e.g., Vickers et al. 1972). IT, the only index of mental speed that does not involve either motor (output) components or executive cognitive processes (meta-processes), is held to tap individual differences in the “speed of apprehension,” the quickness of the brain to react to external stimuli prior to any conscious thought. Meta-analysis results suggest that IT is correlated at approximately .54. In sum, many different ECTs, ostensibly tapping different stages of processing (such as encoding, STM scanning, and LTM retrieval) have been used to investigate the relationship between RT and intelligence. Each of the ECTs discussed has been found to have modest, but reliable (negative) correlations with intelligence, typically in the range of .30 to .50. The correlation between these ECTs and intelligence may, in fact, be somewhat higher after correction for the attenuating effects of restriction of range and measurement error. Multiple correlations between intelligence and various measures of RT are approximately .60. Jensen (2006) convincingly argued that further advances in mental chronometry will depend in large part upon standardization of chronometric apparatus and testing procedures to eliminate the potentially confounding effects of method variance.